This invention relates to a process for preparing a polymer emulsion containing colloidally suspended therein an interpenetrating polymer network wherein a first polymer network is intertwined on a molecular scale with a second polymer network and optionally additional polymer networks. The polymer emulsion of this invention is useful as a binder of fibers or fabrics, especially fiberfill.
Fiberfill is a generic term used to describe a variety of nonwoven fabrics for a variety of end uses. The common feature of all fiberfill products is a measure of loft or thickness in the fabric. This loft is a characteristic of value because it imparts insulation to outerwear and bed quilt stuffing, cushioning in furniture padding, dust holding capacity to filter media and resiliency to scrubbing pads. The most common construction of a fiberfill product is a loosely garnetted, cross-lapped or air laid web of 6 to 30 denier polyester staple fibers which is bonded (locked in its particular fiber arrangement) by an emulsion polymer binder. Fiberfill products can be made with other fibers, e.g. polyamide, cellulose acetate, rayon, glass, alone or in blends with each other. Some fiberfill is sold without a bonding agent but the material will lack durability, tensile strength and resiliency when compared to a bonded product. Bonding methods other than emulsion polymers, such as needle punching, and meltable fibers and powders are also used, but the polymer emulsion method produces the optimum strength/loft ratios for the majority of fiberfill markets.
The polymer emulsion product used as the binder is usually one of the following chemical types: polyvinylacetate, acrylic copolymers, styrene-butadiene copolymers or polyvinylchloride. Polyvinylacetate is the most common binder and in recent years it has been made white enough and strong enough to replace most of the acrylic polymer traditionally used. Polyvinylchloride is used where flame resistance is of prime concern and styrene-butadiene copolymers are used for special rubbery applications.
The characteristic of initial loft is unaffected by the chemical type of the binder used. However, initial loft is not the loft of value. Fiberfill products in their normal use are compressed, reducing the initial loft, and released many times. The true value of loft is how thick the fiberfill web is after repeated compression/recovery cycles. One drawback of current polymer bonded fiberfill technology is that temperatures over 100.degree. F. will soften the binder and cause the fiberfill product to permanently lose loft if it is compressed at this elevated temperature. Temperatures of up to 180.degree. F. are encountered in the shipping and use of many fiberfill products. Typically a fiberfill product, which may lose only 15% of its initial loft if compressed and released at 80.degree. F., will lose more than 80% of its loft if tested the same way at only 120.degree. F. Higher temperatures are expected to even more dramatically damage this loft recovery.
In the preparation of a coated cellulosic web, e.g. a paper web, there is used a pigment, such as clay or the like, sometimes with other materials such as, for example, a soluble pyrophosphate which may act to disperse the pigment in water and stabilize the pigment in water. This mixture, commonly termed a pigment "slip" or, since it usually contains clay, a clay "slip", is then compounded with a binder or adhesive material to produce a composition known in the art as a coating "color", which is useful for coating a cellulose web, e.g. a paper or paperboard web. Substantial quantities of the binder are used, and, accordingly, the composition and characteristics of the binder are of great importance in determining the qualities of the finished coated web. It is important that the binder contributes to the coating or the finished coated web a high degree of brightness, smoothness and gloss, and a good finish and feel after calendering. In addition to these basic qualities required in coatings, the coating color must flow smoothly and evenly so that it can be applied to the cellulosic web at sufficiently high speeds to be economical in ordinary coating processes; and the coating must have high strength, to permit subsequent printing on the coated paper without "picking," i.e. it must have good "pick" characteristics.
Polymer emulsions are useful as a coating binder for paper and paperboard. Paper is coated to provide a smoother surface with increased strength, whiteness and absorbability in order to provide a better surface on which to print. Coating formulations for paper and paperboard can contain a variety of binders including all-latex binders, protein-latex binders, all-starch binders or latex-starch blends. The end use of the paper and, in particular, the method by which it will be printed, may determine which binder type is used in the coating. The major printing method is the offset method in which both water (fountain solution) and an oil based ink are applied to the paper coating. The rate of absorption of the water layer and the ink into the coating is critical to producing a desirable high quality printing.
Styrene-butadiene copolymers are commonly used latex binders, followed by polyvinylacetate, vinylacetate-acrylic copolymers, ethylene-vinylacetate copolymers and all acrylic polymer emulsions. Styrene-butadiene and vinylacetate binders are widely used because of their low cost. The major drawback of styrene-butadiene binders is the poor water absorption giving high SIWA brightness values. High SIWA (simultaneous ink and water absorption test) brightness values mean the coating did not absorb the initially applied water layer and the subsequent ink application failed to penetrate this layer and absorb into the coating. The incomplete ink coverage produces a weak or spotty image. Vinyl acetate binders are often too water absorbent, resulting in press roll fountain solution milking. This problem is the converse of the high SIWA brightness problem. Fountain solution milking occurs when the coating absorbs so much water (fountain solution), that the coating becomes solubilized in the fountain solution and the binder and clay so dissolved give the solution a "milky" appearance. This condition can be predicted by the Adams Wet Rub Test.
Another area in which polymer emulsions are useful is in a coating especially as a binder for industrial and architectural coatings. Industrial and architectural coatings are applied to surfaces of all types, such as metal, wood, concrete, stone, plastic, plasterboard, glass and the like, to provide protection and decoration. Polymer emulsions are now used by industry as the binder of choice in a great variety of waterborne coatings because they are environmentally very desirable. Since solvent emissions into the atmosphere are a major concern, waterborne coatings are preferred to reduce such solvent emissions. Although organic solvent based coatings can still be used, these coating systems have become increasingly uneconomical, because expensive anti-pollution devices, such as afterburners or solvent recovery devices, have to be installed.
In architectural coatings which are for exterior coatings acrylic polymer emulsions dominate, because they have been used for many years and their outdoor properties such as ultraviolet resistance and lack of embrittlement with time have been proven on test fences and in actual practice for many years. Other polymer emulsions such as vinyl acetate-ethylene-vinyl chloride terpolymers have also found increasing use in outdoor architectural coatings because they have also shown to possess excellent properties. Indoor architectural coatings mostly contain vinyl acetate-ethylene copolymer- or vinyl acetate-acrylic copolymer emulsions.
The polymer emulsions that are used for industrial coatings include polyvinyl acetate and polyvinyl acetate copolymers for wood panel finishes, because they can be sanded better than most acrylic coatings. Polyacrylates are used in maintenance coatings for metal tanks and pipes, and as primers for automobiles. These are often deposited by electrocoating processes. Furniture finishes, appliance coatings and the like are also based on polyacrylates. There are some areas in the industrial coatings field where polymer emulsions have not yet been successfully used such as in coil prime- and top coatings. Coil coating primers are applied to continuous coils of bare metal, such as steel or aluminum stock, to protect the uncoated metal prior to fabricating the primed metal. Often a top coat is also applied so that the metal sheet is completely coated prior to sending it to a metal fabricator who converts it to useful metal products It is important for coil coatings to withstand the rigorous fabricating process, when the coated metal is converted to articles such as metal cabinets and the like, without damaging the previously applied coating. The coated metal is often bent and drawn during the fabricating process and therefore must possess toughness and extensibility. Many coatings will separate from the metal in places during this process which often necessitates an expensive refinishing procedure. Although solvent-based coil coatings have been used predominantly in the past, economics and environmental considerations dictate that aqueous coil coatings, primers as well as topcoats, are most desirable for industrial use.
The polymer emulsion prepared by the process of this invention provides a binder compound for fiberfill which provides improved resiliency and loft recovery to the bonded fiberfill products. This polymer emulsion is useful in bonding textile fibers in a fiberfill product or in any nonwoven product or even any traditional woven or knitted textile fabric. The polymer emulsion can also be used in a coating, especially as a coating binder for paper and paperboard. Other types of coatings in which the polymer emulsion is useful include the various industrial coatings such as maintenance coatings (e.g. for metal tanks, pipelines and other metal structures), coil coatings, can coatings, appliance coatings (e.g. for refrigerators, washing and drying machines), wood coatings (e.g. wood panels or furniture), floor coatings and sealers (e.q. floor polishes), automotive coatings (e.g. primers, top coats), leather coatings, concrete sealers and coatings, marine coatings, as well as architectural coatings such as house paints, both exterior and interior.